Electronics devices (e.g., cell phones, smart phones, wireless-enabled portable computing devices) that incorporate radio frequency (RF) components may require complicated and time-consuming RF tuning before they are able to be properly tested and assembled. As illustrated in FIGS. 1A and 1B, a plurality of devices under test (DUT) 104 may be connected to a device interface board 102. The DUTs 104 may be connected to the device interface board 102 via sockets. The device interface board 102 interconnects ports 106 of the DUTs 104 to a plurality of testing resources 110, which may include analyzers and processors. The device interface board 102 may also be known as a loadboard. While FIG. 1A illustrates a plurality of DUTs 104 on a device interface board 102 comprising tuning elements 108, FIG. 1B illustrates exemplary tuning elements 108 placed between a DUT 104 and one or more testing resources 110. The DUTs 104 may be located a fixed distance apart with fixed cabling distances between the testing resources 110 and each port 106 of the DUTs 104. Each port 106 of a DUT 104 will require a separate RF tuning process.
As also illustrated in FIGS. 1A and 1B, each port 106 of a DUT 104 is interconnected to the testing resources along with a plurality of tuning components 108 (e.g., capacitive and inductive elements) that may be placed into the circuit between the particular ports 106 and the testing resources to ensure that a desired impedance of the circuit is reached. An impedance mismatch between a DUT 104 and the testing resources 110 may result in an improper power measurement (due to RF energy bouncing back on the RF line because of the impedance mismatch). Tuning components 108 are capacitors and/or inductors that may be soldered into RF pathways between individual ports and testing resources. As discussed herein, the tuning components 108 may be selected such that the DUT 104 impedance is matched to the testing environment impedance. For example, when a DUT 104 with a desired 50 ohm impedance is connected to testing resources via a device interface board 102, the resulting impedance of the testing system may be other than the desired 50 ohms. Therefore, tuning components 108 of the desired capacitance/impedance values may be placed close to the DUT 102 undergoing RF tuning to ensure that the DUT 102 is matched to the testing environment impedance. An optimal testing environment will imitate the environment that the DUT will experience.
The RF tuning (or impedance matching) of a port 106 to the testing environment may follow one or more RF tuning design approaches. For example, graphical RF tuning designs may utilize a Smith Chart methodology. An exemplary, simplified Smith chart is illustrated in FIGS. 2A-2F. When using a Smith Chart, it is usually assumed that the electrical locations of the tuning elements 108 are known and that component behavior is ideal. However, as discussed herein, in a typical device interface board 102 environment, RF tuning element locations 108 may be spread out because of layout constraints, and a monitoring network analyzer may also be displaced a significant distance from the RF tuning elements 108, with various other kinds of components (e.g., baluns and switches) placed in-between.
These RF tuning component location uncertainties along with path losses and non-ideal component behaviors due to parasitics, may effectively render useless any Smith Chart approach for RF tuning. The distance between the DUT and the testing resources also produces latency problems which renders the Smith chart approach even more inadequate. Therefore, because a strictly-graphical RF tuning design approach is impracticable, other approaches are needed.
The above-described graphical RF tuning process is often replaced by time-consuming, trial-and-error methodology. Such trial-and-error RF tuning processes tend to be highly empirical, serial, and time intensive. For example, when following a trial-and-error process, one or more RF tuning elements 108 are laboriously varied over time until adequate RF tuning element matches are achieved for each RF path (that is, for each port 106 of the DUT 104). As the number of RF ports 106 for wireless devices increases, the complexity and time required to achieve optimal RF tuning increases undesirably.
Not only is such trial-and-error costly and inefficient, it can also damage the DUT because of constant heating and reheating of the circuit board while populating and removing the various tuning elements. This damage can not only render the DUT inoperable, but may result in a DUT that does not act as an undamaged DUT, such that the testing would be faulty and unreliable.
What is therefore needed is a method and apparatus to more accurately and methodically tune the RF port.